The present invention relates to a device for calculating a discrete moving window Fourier transform, that is to say a discrete Fourier transform (DFT) applied to a signal through a window moving or sliding in time. The invention also relates to the application of this calculating device to a radar system.
As is known, numerous applications use calculation of the Fourier transform and, among them is, the filtering operations which are performed in a radar system on the received signal. Furthermore, present technical and technological developments lead more and more to searching for digital solutions for this processing. In this search, one of the difficulties is the required calculating power. This problem is particularly acute in applications such as radar systems where the calculations must be made in real time.
The present invention provides a device for calculating a discrete Fourier transform, in a moving time window, for reducing the number of operations needed.
Accordingly, an object of the invention is to provide a device comprising an assembly of circuits receiving samples (x.sub.m) of the input signal, the output signal of the assembly being applied to one or more identical stages (N). The preceding assembly of circuits comprises a circuit, a shift register for example, conferring a delay of N sampling periods on the incident signal and an adder, performing the subtraction: EQU .delta..sub.m =x.sub.m+N -x.sub.M ( 1)
of the input and output signals of the shift register. Each of the stages delivers a signal X.sub.k.sup.m+1 of the form: EQU X.sub.k.sup.m+1 =(X.sub.k.sup.m +.delta..sub.m).exp {j.2.pi..(k/N)}(2)
where k is the index of the stage (0.ltoreq.k&lt;N).
A further object of the invention is to provide an application of this device to pulse compression in a radar signal processing chain.